Not nute burn. Extreme hunger. Calcium deficiency (water possibly too soft?). Too much stretch due to red spectrum light instead of blue.

Add blue-spectrum light from 'daylight' flourescents right near the plants or from a Metal Halide lamp. This is better for vegging. HPS makes young plants stretch.

You NEED to feed the plants! Use a cannabis-specific fertilizer like Botanicare or Canna- there are many on the market. HAve your tap water tested for hardness at the grow shop and if it is below about 200ppm you will need to add calmag plus up to 250ppm to make up for the lack of calcium in the water. If you want to avoid this, use a potting soil that has plenty of lime in it and make sure to re-pot FREQUENTLY into just SLIGHTLY larger pots.

DO NOT flush those plants at this point; they are already starving.